High-frequency coupling device



A. CROSSLEY ET AL HIGH FREQUENCY COUPLING DEVICE Filed April 10, 1954 pi lmmv' slaullmmgl INVENTORS, ALFRED CROSSLEY, HERBERT E. MEI/VEMA,

ATTORNEY.

Patented May 28, 1935 UNITED STATES PATENT OFFICE HIGH-FREQUENCYCOUPLING DEVICE Application April 10, 1934, Serial No. 719,905

4 Claims.

This invention relates broadly to high-frequency communication systems,and more particularly to receiving systems designed to be operated atcommunication frequencies, examples being those in- 5 tended for radiobroadcast reception or for carrier reception. Such systems, in general,include, in addition to an antenna-ground system, one or more resonantsystems consisting of two inductance coils arranged in magnetic relationto each other, one of the coils being shunted by a variable tuningcondenser. The condenser is normally of a. type having very low losses,and therefore the eiilciency of the complete design depends to a verylarge extent upon the losses in the inductance coils.

A principal object of this invention is to provide a novel type ofcoupling means for use in such receiving systems, which, because of itsdesign, will greatly increase the eficiency of the system. This objectis attained in part by using iron-cored inductances having new andhighly desirable attributes. The cores which we use in these inductancesare ferro-magnetie and consist of finely-divided individually-insulatediron particles compressed with a binding material to make a core body.Cores or" this type, suitable for use at high frequencies, are disclosedin U. S. Patents Nos. 1,940,228 and 1,982,689, and have recently beendescribed in numerous publications in the United States and abroad. Thecombination of such a core with a suitable winding is to be designed inaccordance with" Patent No.

1,978,563, issued Oct. 30, 1934, to Alfred (.lrossley and Charles C.Neighbors, for Improved high-irequency inductance. The inductanceconsists essentially of a tubular cylindrical core of the typedescribed, with a pancake universal winding at its center, the length.of the winding being usually from three-eights to two-thirds of theradial depth, the length of the core being from 2%; to 5 times thelength of the Winding.

Still a further object of the invention is attained by so fashioning theinsulating frame or support on which the inductance coils and theircores are mounted, that it will constitute a single and integral entityembodying all of the features mionic relay. In order to transfer energyfrom the first circuit to the second, the coils may be coupledmagnetically and thus form a transformer, or they may be coupledcapacitively by means of a small condenser connecting theirhigh-potential ends, or a combination of magnetic and capacitivecouplings may be used in order to obtain more uniform gain andselectivity over the desired band of frequencies.

The coil in the antenna-ground circuit, or the first thermionic relayoutput circuit is usually called the primary, and the coil in the inputcircuit of the (second) thermionic relay is usually called thesecondary. In some instances, however, these designations may bereversed, and the thermionic relays may, in certain types of apparatus,be arranged so that they do not operate strictly as amplifiers. Thesevariations, however, are not material with respect to the applicationand scope of the present invention. The variable tuning condenser isusually shunted across the coil here designated as the secondary coil.

In present-day designs, coupling devices of the class here underconsideration normally employ two magnetically coupled air-coreinductances. By suitably designing the primary and second- ,arywindings, and by adjustment of the tuning condenser, the system may betuned to be resonant at the desired frequency. In order to efiect amaximum transfer or" energy between the primary and the secondary, it isessential that the magnetic coupling between the two windings shall beclosely of the optimum value. In pres ent designs, it is normal toestablish the degree of coupling in the design of the transformer, sothat when the coils are assembled the proper coupling will exist.

Because of the losses which normally exist in air-core coils of the typenow commonly used, it is'not essential to provide means for adjustingthe coupling between the primary and secondary coils after the unit isassembled. It is usually sufiicient to determine experimentally whatphysical relation between the two coils will give approximately thecorrect coupling and then to mechanically design the coupling device soas to produce this relation.

in the designs herein described, the losses in the coils themselves aregreatly decreased, and it therefore becomes desirable to provide meansfor accurately adjusting each coupling device to the desired couplingbetween primary and secondary. The present invention, therefore,includes designs employing coils having greatly increased eiiiciency,and arrangements whereby two such coils may be magnetically related inacoupling device with means for producing an accurate adjustment of themagnetic coupling between the windings.

Because of the higher efficiency of iron-core coils, it is possible toobtain greater energy transfer with less coupling than is permissiblewith air-core coils. This results in'an increase in the electricalemciency of thecoupling device. For example, one embodiment-pf theinvention uses about 20% magnetic coupling'between the coils and acoupling condenser ofv 8.5 micromicrofarads; When used with aZOO-micromicrofarad antenna, this antenna coupling device gives a gainof about 20 in-com'parison with a gain of about '9 obtainable withair-core coils, at frequencies between 550 and 1500 kilocycle'sl,

The invention will be better understood by reference to the accompanyingdrawing, which is illustrative of one possible mechanical embodiment ofthe invention and in which- Fig. 1 is an elevation of a high-frequencycoupling device employing ferro-magnetic core bodies;

Fig. 2 is a bottom view of the coupling device shown in Fig. 1;

Figs. 3 and 3a present simplified schematic wiring diagrams whichillustrate methods of employing the couplingdevice of this invention inthe circuits of a high-frequency receiver.

Referring to Fig. 1, the coupling device here illustrated consists of aflanged insulating base I, preferably of a molded phenolic compound suchas bakelite. The base i is designed to be conveniently secured to thereceiver chassis 2 by means of the non-magnetic threaded stud 3 and thenut 4, said stud 8 being preferably molded into the base I. A spindlela, preferablyconsisting of a molded phenolic compound, such asbakelite, receives the hollow cylindrical ferromagnetic core 5 of theprimary winding 6, and the hollow cylindrical ferro-magnetic core 8 ofthe secondary winding 8. These cores are held firmly in place by asuitable cement 9, and may be adjacent each other or be spaceda.suitable amount to approximate the desired degree of coupling. F

For use inthe frequency band. between 550 and 1500 kilocycles, theprimary coil 6 for an antenna coupling device may have an inductance ofabout 1.25 millihenries and be resonant with a normal 200 M. M. F.antenna at-a frequency below the desired band of frequencies, as,

. for example about 315 kilocycles, thereby producing the minimum effecton the gain within the desired band of frequencies. If the device is tobe used to couple'two thermionic relays, the primary inductance may beabout 3.2 millihenries. The secondary coil 8 in either type may have aninductance of about 250 microhenries so as to cover the desired band offrequencies when tuned by a variable condenser having a maximum capacityof about 365 micromicrofarads. The cores 5 and I are secured to thespindle in by means small core is used. This choice may be foundadvantageous in those cases where cost is an important consideration.

Referring-to Figs. 1 and 2,.terminals l0 extend downward from the baseI, being preferably eyeletted through square holes in the base I. Eachlead H- from the coils 6 and 8 extends through an eyelet and is solderedto a terminal l0. Coupling condenser I2 is mounted un rneath the base Iby soldering it to the two ter als 40 which connect to thehigh-potential ends the coils 6 and 8. This condenser may have acapacity of 15.0 micromicrofarads foran interstage coupling deviceintended for use with thermionic relays in the frequency band between550 and 1500 kilocycles. In this case, about 8% magnetic couplingthermionic relay 86. The primary coil 6 is connected between the antennaand ground; The secondary coil 8 is'connected in parallel with thevariable condenser H to form a resonant circuit in the grid circuit ofthe thermionic relay I6.

Fig. 3a shows a coupling device. of the type herein contemplatedconnected between the output circuit I8 of the thermionic relay I9 andthe input circuit 5 of the thermionic relay it. The

it may be arranged to be primary coils B is connected in series with theanode of the thermionic relay ill. The secondary coil 8 is connected inparallel with'the variable condenser H to form a resonant circuit in thegrid circuit of the thermionic relay i6.-

A combination of magnetic and capacitive coupling is especiallydesirable in coupling devices designed for use over a band offrequencies, since it gives much more uniform gain and selectivity thancould be obtained with either magnetic or capacitive coupling alone.Capacitive coupling between the primary and secondary circuits isobtained by means of the condenser i2. The exact degree of magneticcoupling obtained is determined by the relative positions of the coresSand I and their respective coils 6 and 8, and may be adjusted afterassembly but before the cores 5 and 1 are cemented to the spindle Ia, bysliding the core l axially upor down. I i I In employing transformers inaccordance with this invention in the antennastage of broadcastreceivers, it is preferable to so connect them that the magneticcoupling and the capacitive coupling i will be additive. In interstageuses, however, tha connections are preferably such that the magnetic andthe capacitive couplings are in oppo sition. I I

' Certain specific design data and constants have been given to completethe description of .the present invention. It should be understood,however, that these constants are mentioned merely by way of example indescribing certain specific embodiments which in practice have provedsatisfactory, and are not intended to suggest any specific limitationsas to the scope of this invention:

Having thus described our invention, what -w claim is:

I. A high-frequency coupling device including a concentrated primarywinding and a concentrated secondary winding, a term-magnetic core foreach of said windings, said primary winding having a natural frequencylower than any frequency to which said secondary winding is intended tobe timed, said cores being adjacently and coaxially disposed andrelatively adjustable, whereby the electro-magnetic coupling betweensaid primary winding and said secondary winding may be convenientlyadjusted to any desired value within the range of said device.

2. A high-frequency coupling device including a central insulating post,a flange extending radially from said post, compressed comminutedterm-magnetic cores mounted upon said post, a primary winding mountedupon one of said cores, a secondary winding mounted upon another of saidcores said primary Winding having a natural frequency lower than anyfrequency in the range through which said secondary is intended to betuned.

3. A high-frequency coupling device including two coils wound upon andsecured to compressed comminuted tubular magnetic cores, said coresbeing mounted coaxially upon a mandrfl having an insulating radialflange with terminals adapted to be connected to the ends of said coils,one of said coils having a natural frequency lower than any frequency towhich the other coil is intended to be tuned.

4. A support for the ferro-magnetic cores and the terminals of ahigh-frequency transformer in a signaling device, including a horizontaldisc having perforations into which said terminals may be secured, anintegral downwardly extending post having inserted therein a metal studfor securing said support to the frame of said signaling device, and aseparate upwardly extending insulating post for coaxially supportingsaid cores.

ALFRED CROSSLEY. HERBERT E. MEINEZMA.

